1. Field of the Invention
The present invention relates to a wheel spin control apparatus for use in an automotive vehicle for quickly and efficiently restraining the excessively large spin which occurs in driven wheels at the time of a start or during an acceleration of the vehicle. More particularly, the present invention relates to a wheel pin control apparatus which restrains the excessively large spin by the control of the brake system of the driven wheels and/or by the control of the engine.
2. Description of the Prior Art
When the rotation speed of the driven wheels of an automotive vehicle (hereinafter referred to as vehicle) is slightly faster than the speed of the vehicle, i.e., when the driven wheels spin slightly, the driving forces of the driven wheels are efficiently transmitted to a road surface, thus making it possible to drive the vehicle as desired. When the vehicle is started suddenly, accelerated suddenly or driven on a slippery road surface, the driven wheels spin in an excessively large amount, which results in the loss of the driving force of the vehicle, i.e, the engine power will not be efficiently transmitted to the road surface. Wheel spin control apparatuses have hitherto been suggested to reduce such an excessively large amount of a wheel spin to an optimum amount.
According to one prior art wheel spin control apparatus, the rotation speeds of each of driven and non-driven wheels are calculated so as to detect an excessively large amount of a spin. Upon detection of the occurrence of the spin, a braking force is applied to a driven wheel to restrain the spin. For example, according to Japanese Patent Laid-open Publication No. 16164/1986, the increase or decrease of a braking force to be applied to a driven wheel is controlled by detecting the spin amounts and accelerations of the driven wheels and, further, by comparing them with respective threshold levels.
According to prior art apparatuses for controlling the excessively great amount of a spin, the increase or decrease of a braking force to be applied to the driven wheels is determined mainly by the accelerations of the driven wheels rather than the spin amount thereof. For example, in a case where the spin amount exceeds a threshold to a great extent, if the driven wheels are accelerated slightly (for example, if it is smaller than a threshold) it is so controlled that the braking force is reduced; and if the driven wheels are accelerated in an appropriate range (for example, if it is greater than the threshold level), it is so controlled that the braking force is increased. Therefore, when an excessively large amount of a spin or an excessively small amount of a spin (excessive reduction of spin amount caused by the application of braking force to a great extent) is detected, the braking force is increased or decreased continuously, as long as the spin amount or the acceleration of the driven wheels is above the threshold levels.
As discussed above, according to the prior art apparatus, the excessive amount of spin is detected based merely on the spin amount of the driven wheels. Although the acceleration of the driven wheels may be detected, it is not used together with the detected amount of spin to detect the excessive amount of spin. In other words, according to the prior art, to control the excessive amount of spin, no consideration is given to the fact that the excessive amount of spin varies with respect to the acceleration of the driven wheel or with respect to the rate of change of the spin.
Therefore, according to the prior art apparatus, the braking force to be applied to the driven wheels is increased as long as the detected spin amount exceeds its threshold, or as long as the detected acceleration exceeds its threshold.